Scolytus intricatus (European oak bark beetle)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Plant Trade
- Wood Packaging
- Environmental Impact
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Scolytus intricatus (Ratzeburg, 1837)
Preferred Common Name
- European oak bark beetle
Other Scientific Names
- Eccoptogaster intricatus Ratzeburg, 1837
- Eccoptogaster simmeli Eggers, 1923
- Scolytus lenkoranus Eggers, 1942
- Scolytus penicillatus Reitter, 1913
- Scolytus picicolor Stephens, 1830
- Scolytus simmeli (Eggers, 1923)
International Common Names
- English: bark beetle, oak; oak bark beetle
- Spanish: barrenillo de la encina
- French: scolyte du chene
Local Common Names
- Denmark: egebarkbille
- Finland: mantokuoriainen, tammen
- Germany: Eichensplintkäfer; Splintkaefer, Eichen-
- Italy: scolito della quercia
- Netherlands: eikespintkever
- Norway: eikesplintborer
- Sweden: eksplintborre
- SCOLIN (Scolytus intricatus)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Scolytus
- Species: Scolytus intricatus
Notes on Taxonomy and NomenclatureTop of page
DescriptionTop of page
Scolytidae eggs are smooth, ovoid, white and translucent. They are approximately 1 mm long and individually deposited on opposite sides of the egg gallery.
All scolytidae larvae are similar in appearance and difficult to separate. They are white, 'C'-shaped and legless. The head capsule is lightly sclerotized and amber with dark, well-developed mouthparts. Each abdominal segment has two to three tergal folds and the pleuron is not longitudinally divided. The larvae do not change as they grow.
Scolytid pupae are white and mummy-like. They are exarate, with legs and wings free from the body. Some species have paired abdominal urogomphi. The elytra are either rugose or smooth, sometimes with a prominent head and thoracic tubercles.
Beetles of the genus Scolytus are characterized as follows: the eyes are slightly emarginated; the antennal club is large and oval with sutures medially bowed in an acute angle; the pronotum is large; the anterior is constricted; the post and lateral margins are sharply bordered; the elytra are flat with the abdomen rising posterior from the second sternite to the apices; the tibiae are laterally smooth and possess a long curved distal tooth; and the third tarsal segments are bilobed (Grüne, 1979).
S. intricatus has the following distinguishing characteristics: the posterior margins of the second, third and fourth sternite do not posses lateral teeth; the fourth sternite has a small medial process; the head of the males is flat, with dense setae; the overall length ranges from 2 to 3 mm; and the body colour is black with reddish-brown elytra and light-brown antennae and legs (Grüne, 1979).
DistributionTop of page
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 17 Feb 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Federal Republic of Yugoslavia||Present||Native||Invasive|
|United Kingdom||Present||Present based on regional distribution.|
Risk of IntroductionTop of page
All life stages can be dispersed long distances via the movement of wood products including unprocessed logs and lumber, wooden crating, pallets and dunnage, containing strips of bark. S. intricatus was intercepted in dunnage at USA ports of entry 11 times between 1985 and 2000 (Haack, 2001).
North American oak forests are already under attack from several indigenous and introduced pests, including oak wilt (caused by the fungus, Ceratocystis fagacearum), a complex of biotic and abiotic factors leading to oak decline, defoliation by the gypsy moth, Lymantria dispar, and the recently discovered sudden oak death, caused by Phytophthora ramorum in California and southern Oregon. Increased mortality in oak forests due to the introduction and establishment of S. intricatus could lead to further stress on an already stressed ecosystem. Similar damage could occur if this insect appears in Asia.
HabitatTop of page
Hosts/Species AffectedTop of page
In laboratory tests, S. intricatus adults fed on the shoots of species of Aesculus, Alnus, Betula, Carpinus, Castanea, Eleagnus, Fagus, Juglans, Liquidambar, Morus, Prunus, Quercus, Salix and Ulmus (Doganlar and Schopf, 1984).
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page
SymptomsTop of page
Entrance and exit holes may be present and accompanied by boring dust. All life stages occur under the bark except when the adults are seeking new host material for breeding or shoots for maturation feeding. Egg galleries can be found underneath the bark and are constructed perpendicular to the wood grain. Egg niches occur along both sides of the egg galleries. The larval galleries tend to vertically orient with the grain of the wood and can extend from 10 to 15 cm (Yates, 1984).
Evidence of adult maturation feeding may be found on the twigs, usually at the juncture of the current-year and 1-year-old growth (Munro, 1926; Lekander et al., 1977; Yates, 1984).
List of Symptoms/SignsTop of page
|Leaves / yellowed or dead|
|Stems / gummosis or resinosis|
|Stems / visible frass|
|Whole plant / frass visible|
|Whole plant / plant dead; dieback|
Biology and EcologyTop of page
The genus Scolytus consists of approximately 55 species of bark beetles found in the forests of Asia, Europe and North America. Several species are considered to be important pests of either broadleaf or coniferous trees. Economically important species that are indigenous to North America include the fir engraver, Scolytus ventralis, the Douglas-fir engraver, Scolytus unispinosus and the hickory bark beetle, Scolytus quadrispinosus (Furniss and Carolin, 1977; Drooz, 1985). Scolytus morawitzi is a pest of larch in Asia. The smaller European elm bark beetle, Scolytus multistriatus, a vector of Dutch elm disease (caused by the fungi Ophiostoma ulmi and Ophiostoma novo-ulmi), was introduced into North America during the early part of the twentieth century and is now present over much of Canada and the USA.
The number of generations per year varies with location. For example, in England, S. intricatus completes one generation per year (Yates, 1984), whereas two generations per year are completed in southern Germany (Kamp, 1951).
S. intricatus typically overwinters in the late larval stages (Lekander et al., 1977; Yates, 1984) or occasionally in the pupal stage (Doganlar and Schopf, 1984). Overwintering and subsequent pupation usually takes place in the outer bark if the bark is over 4 mm thick, or in the outer sapwood if the bark is thin (Lekander et al., 1977; Yates, 1984). Pupation usually occurs in late spring or early summer and lasts for 1 to 2 weeks (Yates, 1984). In England, adult emergence usually spans 2 to 3 weeks and occurs from mid-May to late June, depending on local temperatures (Yates, 1984). S. intricatus has a 1:1 sex ratio at the time of adult emergence (Doganlar and Schopf, 1984; Yates, 1984).
Upon emergence, the adults fly to the crowns of trees, primarily oaks (Quercus spp.). There they undergo maturation feeding on the twigs, usually at the juncture of the current-year and 1-year-old growth (Munro, 1926; Lekander et al., 1977; Yates, 1984). In England, the period of shoot feeding is estimated to last for 2 to 3 weeks, assuming that this was the difference in time between peak adult emergence and peak attack on brood material (Yates, 1984). Doganlar and Schopf (1984) found that S. intricatus adults prefer to shoot-feed on Quercus but they also accepted species of Aesculus, Alnus, Betula, Carpinus, Castanea, Eleagnus, Fagus, Juglans, Liquidambar, Morus, Prunus, Salix and Ulmus in laboratory tests. In addition, Doganlar and Schopf (1984) noted that the shoot feeding did not occur on species of Acer, Celtis, Crataegus, Fraxinus, Liriodendron, Populus and Sambucus. Shoot feeding is not obligatory and newly emerged adults will reproduce if placed directly on freshly cut logs (Doganlar and Schopf, 1984; Yates 1984; Habermann and Schopf, 1987).
After shoot feeding, the adults seek breeding sites, which are usually the trunks and branches (> 5 cm in diameter) of weakened and dying oaks as well as recently fallen branches (Lekander et al., 1977; Gibbs, 1978; Yates, 1981, 1984). In the laboratory, S. intricatus successfully constructed egg galleries in branches that were only 1 to 1.5 cm in diameter (Doganlar and Schopf, 1984). S. intricatus has been reported to breed in oak trees stressed by drought (Gibbs, 1978; Yates, 1984; Novak, 1988; Eisenhauer, 1989), air pollution (Krol, 1982) and insect defoliation (Szontagh, 1984, 1985; Eisenhauer, 1989). In addition, S. intricatus will breed in branches that have been cut 12 to 18 months earlier (Yates, 1984). The pheromone system of S. intricatus has not been determined, but Yates (1984) suggested that the males might produce an aggregation pheromone. Mating may occur on twigs during maturation feeding (Doganlar and Schopf, 1984) or later during gallery formation (Yates, 1984). Adult flight may be limited to less than 100 m (Edelman and Malyseva, 1959). Depending on the location and the number of generations per year, adult activity usually occurs between May and September (Lekander et al., 1977; Yates, 1981, 1984; Doganlar and Schopf, 1984). There is little evidence that the re-emergence of adult parents occurs (Yates, 1984).
S. intricatus is monogamous. Either the males or females can initiate the construction of the egg galleries (Yates, 1984). The egg galleries are constructed perpendicular to the wood grain. The eggs are individually laid in niches that are constructed along both sides of the egg galleries. The average egg batch size was reported to range from 18 to 36 eggs per gallery in studies conducted in England (Yates, 1984). However, in Germany, average batch sizes of 36 to 83 eggs were reported (Doganlar and Schopf, 1984). The adult females typically lay eggs over a 2-week period and then die, usually within their egg galleries (Yates, 1984).
Egg hatch typically occurs from 10 to 14 days post egg lay (Yates, 1984). There are five larval instars (Yates, 1984) or possibly six (Doganlar, 1984). Pupation occurs in cells at the end of the larval galleries.
S. intricatus has been associated with oak decline throughout its geographic range (Szontagh, 1984; Kolk, 1985; Novak, 1988; Pavlik, 1994; Rossnev et al., 1994; Zach, 1994; Markovic and Stojanovic, 1996). In a few studies, S. intricatus adults were contaminated with fungal spores of Ophiostoma spp. at the time of emergence from brood trees (Edelman and Malyseva, 1959; Guseinov, 1984; Srutka, 1996). In other studies, S. intricatus was implicated as the principal vector of the various fungi associated with oak decline in Europe (Kryukova, 1976; Guseinov, 1981; Kolk, 1985; Eisenhauer, 1989; Rossnev et al., 1994). Many experts consider that S. intricatus would be an effective vector of the oak wilt fungus, Ceratocystis fagacearum if either the insect became established in North America or if the fungus became established in Europe (Gibbs, 1978, 1984; Gibbs and French, 1980; Doganlar et al., 1984; Doganlar and Schopf, 1984; Schopf et al., 1984; Yates, 1984).
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page
A study in Slovakia indicated that the Great spotted woodpecker, Dendrocopos major destroyed between 47.7 and 72.9% of the S. intricatus brood in infested oak logs (Pavlik, 1999).
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||adults||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
Wood PackagingTop of page
|Wood Packaging liable to carry the pest in trade/transport||Timber type||Used as packing|
|Solid wood packing material with bark||Oak, other broadleaf trees: crating, dunnage, pallets||Yes|
|Wood Packaging not known to carry the pest in trade/transport|
|Loose wood packing material|
|Processed or treated wood|
|Solid wood packing material without bark|
ImpactTop of page
S. intricatus can invade and kill oaks that have been weakened by oak decline, drought or other stress factors. This insect is one of a number of species involved in European oak decline, a progressive dieback of oaks caused by the interaction of climatic events, disease-causing organisms and insects (Doganlar and Schopf, 1984; Markovic and Stojanovic, 2003). Studies on the fungal associates of S. intricatus suggest that it is the vector of at least two fungi, Ceratocystis piceae and Ophiostoma roboris that are weak pathogens of oaks and part of the European oak decline complex (Eisehauer, 1989; Rossnev et al., 1994; Srutka, 1996).
The European oak bark beetle has also been associated with trees infected by the chestnut blight fungus, Cryphonectria parasitica. This fungus has been recovered from oaks in Italy, which were subsequently infested by bark beetles, including S. intricatus. Fungal spores of C. parasitica were recovered from emerging adults. S. intricatus adults feed in the branches of a number of broadleaf trees including Castanea sativa, which makes it a potential vector of this disease of chestnut (Frigimelica and Faccoli, 1999).
Another potential impact of S. intricatus is as a vector of Ceratocystis fagacearum, the fungus that causes oak wilt disease in North America (Doganlar et al., 1984; Schopf et al., 1984; Yates, 1984). Gibbs and French (1980) suggested that S. intricatus could be a more efficient vector of oak wilt than bark beetles of the genus Pseudopityopthorus, which are vectors of this disease in North America.
Environmental ImpactTop of page
Detection and InspectionTop of page
Similarities to Other Species/ConditionsTop of page
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.Cultural Control
Tree mortality, caused by S. intricatus, can be minimized through the maintenance of healthy, vigorous oak forests. This includes the rapid removal of trees or portions of trees damaged by the wind, ice or snow, or logging debris that could serve as breeding sites, thinning of dense oak forests and the removal of trees with symptoms of oak decline.
The opportunities for biological control of S. intricatus in its geographic range are limited because there is a diverse complex of natural enemies already attacking this insect (Yates, 1984; Capek, 1986; Pavlik, 1994; 1999; Markovic and Stojonovic, 1996, 2003). However, should this insect become established in a new location, some of the more commonly occurring species (e.g. Ecphylus silesiacus) would be candidate species for a classical biological control programme.
The direct control of S. intricatus with chemicals is not considered to be a viable pest management tactic.
Research is underway to study both the host- and insect-produced chemicals that influence host selection and mass attack by S. intricatus. Although some candidate compounds have been identified (Vrkocova et al., 2000, 2003), the use of these materials for monitoring or pest management of this insect has not yet been developed. Therefore, the use of pheromones for the monitoring or management of S. intricatus is not a viable tactic.
Due to the relationship between S. intricatus and European oak decline, monitoring for the two agents should be a co-ordinated effort. Crown symptoms, including thin and wilted foliage, branch dieback and tree mortality can be detected by a combination of aerial and ground surveys.
Integrated Pest Management
Few tactics are available to manage S. intricatus. Therefore, elements of an integrated pest management programme must focus on measures designed to maintain the health and vigour of oak forests. This could be coupled with the timely detection and removal of material that could serve as breeding sites for this insect (e.g. logging debris, damaged or broken trees or trees with symptoms of oak decline).
ReferencesTop of page
Bright DE; Skidmore RE, 2002. A catalogue of Scolytidae and Platypodidae (Coleoptera), Supplement 2 (1995-1999). Ottawa, Canada: NRC Research Press, 523 pp.
Doganlar M, 1984. Number of mandibulae in larval galleries filled with powder post, as a tool for determination of the number of larval instars in bark beetle species (Coleoptera: Scolytidae). Turkiye Bitki Koruma Dergisi, 8(4):225-229
Doganlar M; Schopf R, 1984. Some biological aspects of the European oak bark beetle, Scolytus intricatus (Ratz.) (Col., Scolytidae) in the northern parts of Germany (BRD). Zeitschrift für Angewandte Entomologie, 97(2):153-162; 12 ref.
Duffy EAJ, 1953. Handbooks for the Identification of British Insects. Coleoptera: Scolytidae and Platypodidae. London, UK: Royal Entomological Society of London, 5(15).
Edelman NM; Malyseva MS, 1959. The biology of Scolytus intricatus Ratz. (Coleoptera, Ipidae) in the oak woods of the Savala forest, Voronezh region. Entomologiceskoe Obozrenie, 38:369-381.
Frigimelica G; Faccoli M, 1999. Preliminary report on the occurrence of Cryphonectria parasitica (Murrill) Barr on different tree species in Friuli Venezia-Giulia (Italy). Acta Horticulturae, No. 494:467-472; 17 ref.
Furniss RL; Carolin VM, 1977. Western Forest Insects. Washington DC, USA: US Department of Agriculture Forest Service, Miscellaneous Publication No. 1339.
Grüne S, 1979. Handbuch zur bestimmung der Europäischen Borkenkäfer (Brief illustrated key to European bark beetles). Hannover, Germany: Verlag M & H Schapfer.
Guseinov ES, 1981. Reasons for the dieback of oak. Lesnoe Khozyaistvo, 8:54-56.
Guseinov ES, 1984. Vascular dieback of oak in Azerbaijan. Mikologiya Fitopatologiya, 18:144-149.
Haack RA, 2001. Intercepted Scolytidae (Coleoptera) at US ports of entry: 1985-200. Integrated Pest Management Reviews 6: 253-282.
Habermann M; Schopf R, 1987. Studies on laboratory rearing, emergence of young adults and feeding by adults of Scolytus intricatus (Ratz.) (Col., Scolytidae). Journal of Applied Entomology, 104(5):519-528
Jurc M; Bojovic S; Komjanc B; Krc J, 2009. Xylophagous entomofauna in branches of oaks (Quercus spp.) and its significance for oak health in the Karst region of Slovenia. Biologia (Bratislava), 64(1):130-138. http://www.springerlink.com/content/p225h6575l3v0316/?p=8aeab9fab4af4490be43d60e965b3447&pi=17
Kamp HJ, 1951. Notes on the biology of the oak bark beetle, Scolytus intricatus Rtzb. Anzeiger für Schädlingskunde, 24:85.
Kolk A, 1985. Role of insects in oak dieback. Las Polski, 12:18.
Markovic C; Stojanovic A, 2003. Significance of parasitoids in the reduction of oak bark beetle Scolytus intricatus Ratzeburg (Col., Scolytidae) in Serbia. Journal of Applied Entomology, 127(1):23-28; 25 ref.
Munro JW, 1926. British bark beetles. Forestry Commission Bulletin 8, 1-77.
Pavlik S, 1994. The effect of extreme site conditions on the desiccation of oaks and damage by woodpeckers. Lesnicky Casopis, 40:153-158.
Pavlik S, 1999. Predation of overwintering larvae of the European oak bark beetle (Scolytus intricatus Ratz.) by woodpeckers at logging residues in oak forests. Acta-Facultatis-Forestalis-Zvolen -Slovakia, 41:305-313.
Roganovic D, 2012. Bark beetles (Scolytidae, Coleoptera) of beech (Fagus moesiaca Domin, Maly/Czeczott.) in Mt. Komovi area-Montenegro. Agriculture and Forestry [An International Conference entitled "Role of Research in Sustainable Development of Agriculture and Rural Areas", Podgorica, Montenegro, 23-26 May 2012.], 57(4):35-42. http://www.btf.ac.me
Schedl KE, 1981. Familie: Scolytidae (Borken- und Ambrosiakäfer). In: Freude H, Harde KW, Lohse GA, eds. Die Käfer Mitteleuropas. Vol. 10. Krefeld, Germany: Goecke & Evers, 34-99.
Schopf R; Stramm J; Doganlar M, 1984. On the possible transmission of the oak wilt fungus (Ceratocystis fagacearum) by insects in the northern part of Germany. Forstarchiv, 55:103-106.
Srutka P, 1996. Transmission of fungus spores by bark beetles of the genus Scolytus with respect to the oak bark beetle (Scolytus intricatus Ratz.). Lesnictvi - Forestry, 42(11):510-517; [English figures and tables.]; 8 ref.
Vrkocová P; Kalinová B; Valterová I; Koutek B, 2003. Analysis of European oak bark beetle (Scolytus intricatus) extracts using hyphenated and chiral chromatography techniques. Talanta, 59(1):107-114; 19 ref.
Wood SL, Bright Jr. DE, 1992. A catalog of Scolytidae and Platypodidae (Coleoptera), Part 2: Taxonomic Index. Provo, Utah, USA: Bringham Young University, Great Basin Naturalist Memoir No. 13.
Yates MG, 1981. The subcortical fauna of oak; scolytid beetles as potential vectors of oak wilt disease. In: Last FT; Gardiner AS, eds. Forest and Woodland Ecology. ITE Symposium 8. Cambridge, England: Institute of Terrestrial Ecology, 116-117.
Amini S, Nozari J, Mandelshtam M Yu, Knížek M, Etemad V, Faccoli M, 2017. New records of Iranian bark beetles (Coleoptera: Curculionidae, scolytinae) and their host plants. Zootaxa. 4350 (2), 396-400. DOI:10.11646/zootaxa.4350.2.13
Bright DE, Skidmore RE, 2002. A catalogue of Scolytidae and Platypodidae (Coleoptera), Supplement 2 (1995-1999)., Ottawa, Canada: NRC Research Press. 523 pp.
CABI, Undated. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI
Guseinov ES, 1984. Vascular dieback of oak in Azerbaijan. In: Mikologiya Fitopatologiya, 18 144-149.
Jurc M, Bojović S, Komjanc B, Krč J, 2009. Xylophagous entomofauna in branches of oaks (Quercus spp.) and its significance for oak health in the Karst region of Slovenia. Biologia (Bratislava). 64 (1), 130-138. http://www.springerlink.com/content/p225h6575l3v0316/?p=8aeab9fab4af4490be43d60e965b3447&pi=17 DOI:10.2478/s11756-009-0024-8
Marković Č, Stojanović A, 2003. Significance of parasitoids in the reduction of oak bark beetle Scolytus intricatus Ratzeburg (Col., Scolytidae) in Serbia. Journal of Applied Entomology. 127 (1), 23-28. DOI:10.1046/j.1439-0418.2003.00620.x
Nakladal O, 2011. Results of beetles (Coleoptera) survey of Zástudáncí National Nature Reserve (Central Moravia) 2008 - part 2. Casopis Slezského Zemského Muzea (A). 165-178. DOI:10.2478/v10210-011-0017-4
Wood SL, Bright DE, 1992. A catalog of Scolytidae and Platypodidae (Coleoptera), Part 2: Taxonomic Index. In: Great Basin Naturalist Memoirs, 13 1-833.
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